Method of controlling synchronous rectifier metal-oxide-semiconductor with pulse transformer

A method of controlling an isolated power supply comprising a primary side circuit and a secondary side circuit, wherein the primary side circuit comprises a first switch with a first voltage thereon, an auxiliary winding with a second voltage thereon, and a controller, the secondary side circuit comprises a second switch and a pulse transformer, and the method comprises following steps:

• retrieving, by the controller, the first voltage or the second voltage as a specific voltage;
• sensing, by the controller, an oscillation waveform of the specific voltage after the second switch is turned off at a first timing point in a first cycle;
• retrieving, by the controller, a second timing point based on the oscillation waveform;
• and
• controlling, by the controller, the pulse transformer to adaptively adjust a third timing point for turning off the second switch in a second cycle based on the second timing point retrieved in the first cycle;
• wherein the second switch is turned on at a first reference timing point before the first timing point in the first cycle, and the second switch is turned on at a second reference timing point before the third timing point in the second cycle,
• wherein the step of controlling, by the controller, the pulse transformer to adaptively adjust the third timing point for turning off the second switch in the second cycle based on the second timing point retrieved in the first cycle comprises:
• retrieving a first difference between the first reference timing point and the second timing point;
• retrieving a second difference between the first reference timing point and the first timing point;
• defining a third difference via adding the second difference with a first predetermined duration;
• generating a determination result after determining whether the third difference is larger than the first difference in the first cycle;
• adjusting the second difference as a fourth difference based on the determination result;
• and
• controlling the pulse transformer to turn off the second switch at the third timing point, wherein the third timing point is later than the second reference timing point by the fourth difference.